1. Field of the Invention
The present invention relates to an image taking optical system and an image taking apparatus. To put it in detail, the present invention relates to a technical field of typically improving the quality of images by adjusting the spectroscopic characteristic of light incident on an image taking device by making use of a first infrared-ray absorption filter, a multi-layer film and a second infrared ray absorption filter which are provided on an optical path.
2. Description of the Related Art
In recent years, there is a rising demand for quality improvement of image taking apparatus such as digital video cameras and digital still cameras and for downsizing of the image taking apparatus. In order to meet this demand, a high-density CCD (Charge Coupled Device) and/or a high-density CMOS (Complementary Metal-Oxide Semiconductor) device are used as a solid-state image taking device employed in the image taking apparatus and, on top of that, there has been proposed means for typically reducing the size of the image taking optical system.
There are a number of known technologies for improving the resolution of an image taking optical system in order to raise the quality of images in an image taking apparatus employing such a solid-state image taking device.
In order to raise the quality of images, however, it is very important to provide means for assuring good color reproducibility of an image and/or a video as means separated from the improvement of the resolution.
In general, an image taking apparatus employs an optical filter such as an infrared-ray absorption filter and components including lenses. The optical filter and the components including lenses are provided on an optical path, forming an image taking optical system (For example, Japanese Patent Laid-open No. 2006-220873). Thus, in order to implement the ideal color reproducibility, it is necessary to properly adjust the spectroscopic characteristic of the optical filter such as an infrared-ray absorption filter.
In addition, with the reduction of the sizes of the image taking optical system and/or the lens unit, light is reflected by optical members composing the lens unit and members (including a multi-layer film) composing the image taking optical system, becoming stray light. If the stray light hits the image taking device, the color reproducibility deteriorates with ease.
Thus, in order to implement both the improvement of the quality of images and the size reduction, it is important to reduce the amount of stray light incident on the image taking device by preventing the stray light from being generated.